1. Field of the Invention
The present invention relates to adapters for connecting conduits to boxes, fittings, pipes and systems, and more particularly to adapters for adapting nonmetallic conduits to boxes, threaded fittings, threaded pipes and metallic systems.
2. Background Information
Adapters exist for adapting nonmetallic conduits to boxes, threaded fittings and metallic systems. Some adapters have threads on one end and a socket on the other end. Typically a threaded end of a plastic adapter is threaded upon a pipe while a socket or bell end of the adapter receives an end of a conduit. The pipe may have internal or external threads, and the adapter will have corresponding threads to match. The adapter allows the conduit to be securely connected to the pipe. Such adapters are commonly used by electricians who run plastic conduit underground and then connect the conduit to a pipe or electrical box, such as connecting to a metal pipe or metal electrical box, for instance. The conduit is typically glued into the socket or bell end of the adapter.
FIGS. 20-26 show prior art conduit 90 and prior art adapters 92, 94. There are generally two major providers of such adapters in the United States, including providers such Cantex Inc., of Fort Worth, Tex. and the provider of Carlon® products, owned by ABB Asea Brown Boveri Ltd, of Switzerland. Conduit 90 is a hollow tube typically made of plastic or PVC or other material and may come in a variety of lengths and gauges or sizes. In some cases a conduit 90 will span several feet in length, such as 8 feet or 10 feet or 20 feet or even longer. Conduit 90 typically comes in a variety of sizes or “trade sizes” including standard trade sizes such as ½, ¾, 1, 1¼, 1½, 2, 2½, 3, 3½, 4, 5 and 6. Such standard trade sizes will meet industry standards or specifications, such as in one instance where the trade sizes correspond to UL-651 standards and/or NEMA TC-2 standards. Typically one end of conduit 90 has an outer diameter configured to fit comfortably within a “bell” end 91 of the conduit 90 having a slightly larger inner diameter to receive the end of an adjacent like conduit 90. The female end is configured to receive a same or standard trade size conduit while the threaded end is configured to connect to a threaded component of the same or similar standard size component. In some instances a conduit 90 in compliance with standards will exhibit an outer diameter 96 configured to insert into a bell 91 of a like conduit 90 having a bell inner diameter 97 (see FIG. 26). Such standard trade sizes, (at least according to published data for Cantex Schedule 40 Conduit in compliance with UL 651) of conduit 90 in some instances will have the following characteristics (size: outer diameter): size ½: 0.840; size ¾: 1.050; size 1: 0.1315; size 1¼: 1.660; size 1½: 1.900; size 2: 2.375; size 2½: 2.875; size 3: 3.50; size 3½: 4.000; size 5: 5.563; size 6: 6.625. Further, internally-threaded adapters configured to comply with standards are typically fittings intended for joining a length of rigid PVC conduit, a PVC elbow to threaded rigid metal conduit or other externally-threaded devices. Externally-threaded adapters (also referred to as terminal adapters) configured to comply with standards are typically fittings intended for joining a length of rigid PVC conduit or elbow to a) the knockout area of a metal box with a metal locknut, b) a threaded metal hub or fitting on a metal box, c) a threaded hub on a phenolic box, or d) a knockout in a phenolic box.
Several lengths of conduit 90 may be connected together end-to-end to span a desired distance. A length of conduit 90 is often buried in ground so that cables or electrical wires may pass through conduit 90 for protection. In some instances conduit 90 will terminate adjacent a conduit box or pipe 93 or other structure for connection. For instance, a conduit 90 may terminate adjacent a threaded pipe 93 where the conduit needs to be connected to the pipe. Because conduit 90 lacks a threaded end, an adapter 92, 94 is used to connect the conduit 90 to the pipe 93 for instance. A terminal adapter such as prior art male adapter 92 is threaded onto a threaded pipe 93, for instance, and then the bell end 95 of the adapter 92 receives a terminal end of conduit 90. The conduit 90 is glued into the bell end of the adapter 92. In this manner the conduit 90 is secured to the threaded pipe 93. Where the threaded pipe 93 includes internal threads, a male adapter 92 is used; where the threaded pipe 93 includes external threads, a female adapter 94 is used.
There are other types of adapters or connectors for which patents have been granted, such as those shown in U.S. Pat. Nos. 3,783,178 and 3,055,683. While the foregoing adapters or connectors have useful features and some have been the subject of patents, there is room for improvement.